fix nearest_neighbor not serializing weight_manager (refs #62)
fix nearest_neighbor not serializing weight_manager (refs #62)

gintenlabo/jubatus_core,rimms/jubatus_core,gintenlabo/jubatus_core,gintenlabo/jubatus_core,rimms/jubatus_core,rimms/jubatus_core,rimms/jubatus_core,gintenlabo/jubatus_core